Oscillation control means



June 16, 1942. P. PADVA OSCILLATION CONTROL MEANS Filed July 13, 1940 Pm PAW/1 IN VENTOR.

fi 7 gm A TTORNE Y Patented June 16, 1942 2,286,641 OSCILLATION ooN'raoL mums lPhilip Padva, Los Angeles, Calif., a aignor to Cannon & 00., Los Angelou, Calif., a corporation of California Application July 1:, 1940, Serial No. 345,434

5 Claims.

My present invention relates to means for stabilizing a movementwherein undesired sustained oscillations occur, unless inhibited by said stabilization.

The action is somewhat analogous to that obtained in a conventional radio or audio frequency vacuum tube circuit, where the input and output of such circuit are coupled together deliberately, by capacitive, or magnetic, or other means; or incidentally and obtrusively by the stray couplings within the associated tube circuits or within the tube itself of said circuit. Such conditions are effectively suppressed by methods well known in the art; and particularly, the use of resistance at one or more points of the system can be utilized to create a condition of inefilciency that will leave a residue of available energy too small to be capable of sustaining oscillation. This, at the price of emciency.

A similar condition exists when a spot of light, adapted to influence a photoelectric cell, is balanced in a predetermined partly-obscured condition by forces acting on means controlling the movement of the spot, which forces consist of a static or spring force and an opposing amplifled electrical force, the intensity of which is controlled by the illumination of the photoelectric cell by the light. In the instance which is the basis of this application, the link which provides the coupling is the beam of light. This light acts upon the photoelectric cell by suitable means and the amplified output of the photoelectric cell in turn acts upon the beam of light by virtue of moving an element in the associated optical system, i.'e., a reflector or mirror.

It is a main object of my invention to provide means for controlling, to varying degree, the

amplitude of the parasitic oscillatory movement of a member; which means are particularly effece tive when the frequency of this oscillation is of a relatively high order as compared to the velocity of the desired movement. I use the word velocity in a sense such that, were it translated in desired oscillation for effective comparison with parasitic oscillation, the frequency would be comparatively low.

Other objects and advantages of my invention will be found in the description, the drawing, and the appended claims.

For complete understanding of the invention, reference may be had to the following detailed description and accompanying drawing, wherein the single figure is a mainly diagrammatic view of a photoelectric control system embodying my present invention,

In the drawing, the numeral ll indicates a "point" source of light, such as can be obtained by suitably masking the rays emitted by an incandescent element. The rays from the source are refracted and directed by a lens l2, as a beam defined by the lines I3, toward a reflector or mirror ll, the beam being of such area at the mirror as to extend beyond its marginal edges. That portion of the beam impinging upon the mirror is reflected thereby toward an inclined reflector l5 which is curved to conform substantially to the arc of the radius of the reflected beam. From the inclined curved reflector, the ray is directed substantially vertically toward the surface of a chart or graph disk iii, of translucent material, the beam converging to its focal pointat this surface. The inclined mirror can be so formed as to conform to any type of charge ordinate curvature: simple, complex, or rectilinear. The chart is supported by a shaft i'I which is adapted to be rotated ata constant speed, such as one revolution per minute, by motor means (not shown).

Positioned below the disk IE, to receive the rays of the beam which pass therethrough, is an elongated photoelectric cell it which is connected to the input of an electronic amplifier, indicated by the legend. The output of this amplifier is connected by wires I9 to the movable coil 20 of an electromagnetic motor comprising a U-* shaped pole member 2| and'an energizing or field coil 22 therefor. The coil 20 is wound on a frame 23, of insulating material, which is mounted for rotary movement between the poles of the core member on a shaft 24. This shaft is supported by a pivot bearing 25 and carries the mirror It. A cylindrical center core 26, supported by a bracket 21 secured to an arm of the core member 2i, aids the flow of magnetic field flux.

Mounted on lower portions of the shaft 24 are the coil assemblies 28 and 29 of two other electromagnetic devices 30 and 3i, respectively. These devices are similar in construction to the motor described above. The field coils 22, 32 and 33 of the devices are connected in series to a common source 34 of direct current or rectified alternating current. The functions of the electromagnetic devices and It will be described hereinafter.

The shaft 24 is preferably composed of separate sections, but for the sake of simplicity it will be considered as a single shaft. Connecting means 35 and 36 are provided on lower portions of the shaft whereby the planes of the coil assemblies 2| and 29 can be oriented with respect to each opaque line '39. This line is such as is formed by the pan of a recording instrument, the variations in the contour of the line representing change with respect to time, of a condition, such as flow, pressure, or the like. The function of the system comprising the light beam, reflectors It and I5, photoelectric cell l8, its amplifier, and the motor comprising elements to 24, is to cause the light spot to follow the contour ofv the line 39 as the chart disk is rotated. Means responsive to the movement of the light beam may be provided for integrating such movement, but are not'disclosed herein as they form no part of the present invention.

When the photoelectric cell is illuminated, the power produced by the amplified photoelectric current flowing in coil 20 tends to rotate the mirror in a direction such as to move the light spot toward the center of the chart. This movement is in opposition to the bias of spring 38. If the chart is rotated, by manual or other means, in a clockwise direction, as viewed from above, then the line will fall away from the spot, permitting more light to pass to the photoelectric cell. This increased light energy is manifest in increased amplifier output, and the coil 20 controlling the movement of mirror I4, is caused to turn in a direction that will place the spot of light in normal contact at the new portion of the chart line. As the chart l6 continues to turn, the spot will reach a portion of the line which, instead of falling away from the spot, rises toward the periphery of the chart and tends to intrude upon the spot. The spot is then ob.- scured to a greater extent, reducing the light energy falling upon the photoelectric cell I8, and the consequent lessened output of the amplifier permits the bias spring 31 to become more dominant, pulling the spot toward the periphery. The mean proportion of the area of the spot exposed or obscured can be controlled by balancing amplifier gain to spring bias. The action is, of course, not discontinuous as description analysis requires, but is constant and smooth. Throughout the entire range of travel from center to periphery, or vice versa, the spring 31, and the energy resident in coil 20 as controlled by the extent that the spot is obscured or exposed by the chart line, are in balance. The spot thus remains in its balanced position with respect to the line as the chart rotates. However, such conditions only result when the balancing forces employed are relatively small and the chart is rotated very slowly. If the forces are increased to a degree such as will effect rapid movement of the spot in either direction, sustained inward and outward movement (or oscillation) of the spot will be set up, as was described in the introduction to this specification.

Referring again to the oscillating vacuum tube and its associated circuit: oscillation will occur when all the necessary links are present, and it is a moot question as to how the first oscillation is actually initiated. Opinion seems to indicate that thermoelectric eifects, irregularity of filament emission, et cetera, are the probable primal disturbances which prevent the system from remaining stable and non-oscillating when not deliberately disturbed. The application of resistance or load to the circuit, as previously mentioned, will suppress oscillations at the price of efliciency. Likewise, when the chart following system is rendered sluggish by reducing available energy to a point barely above that necessary to supply frictional and other losses, the system will exhibit little or no tendency to oscillate, and, as a consequence, will respond inadequately to the function of tracking the line.

Factors contributing toward parasitic oscillations are the natural sensitivity and rapid response toward which the system is designed; also, the small diameter of the light spot (in the order of 0.010 inch) at the end of a long lever the beam from mirror l4 to mirror IS. The diameter of the light spot is small so as to permit its entrance to the root of acute angles described by the chart line. The chart line followed under actual conditions is far more irregular and possesses amplitudes of greater frequency than those of the relatively simple line 39. Because of the intent of following a complex complete curve within a small period of time, say, one minute, the forces acting upon the physical support of moving mirror ll must be sufiiciently great to permit it to respond with rapidity. This condition, as mentioned previously, is ideal for the setting up of sustained parasitic oscillations; the frequency of these oscillations being dependent upon the moment of inertia, of spring tension, et cetera. If one considers alight spot of 0.010 inch diameter and a chart line of 0.010 inch width, and the spot half obscured at its mean point of range of travel across the chart, a motion of 0.005 inch will entirely obscure the spot from, or reveal it to, the photoelectric cell, thus permitting relatively enormous forces to be set up which will cause the spot to cross the line to a considerable distance beyond and on both sides of the line.

The means which I employ for quelling this undesired oscillatory component of movement of the system will now be described. These means are entirely separate from the electrical system of the line tracker described above, and comprise the electromagnetic devices 30 and 3|, their associated movable coils 28 and 29, and the oscillator control amplifier, indicated by the legend,

which interconnects these coils; the output of the amplifier being connected to the coil 28 through a potentiometer 40. The coils 20, 28 and 29 being each rigidly mounted on the shaft 24, upon movement of the shaft, initiated by the displacement of the spot with reference to the chart line, the coils 28 and 28 are moved; 4

cutting the flux lines produced by the electromagnetic devices 30 and 3|, respectively, and thus each generating an E. M. F. However, the E. M. F. generated in coil 28 is of no material consequence inasmuch as it is overwhelmed by the relatively enormous output of the oscillation control amplifier. The E. M. F. of coil 29 is of basic importance, for it forms the stimulous of the oscillation control amplifier and thus .becomes of dominating influence when the coil 28 receives it. The output of the amplifier is coupled to the coil 28, as by a transformer 4|, so that the direction of the E. M. F. induced in coil 29 is preserved when coil 28 receives it from the amplifier. Also, the coil-28 is so polarized in connection to vthe output of the oscillation control amplifier that its motor reaction in the field of assembly 30 is in opposition to the direction of movement which induces the E. M. F. in coil 29.

Assuming a tendency to oscillate; the slightest motion at the high natural period of shaft 24, and the coils and mirror attached to it, produces an E. M. F. in coil 29, which is amplified in the oscillation control amplifier and applied to coil 28, whose power of reaction is proportionalto the E. M. F. generated in coil 29, and this in turn is a function of the slightest motion re-- ferred to. Thus, the more vigorous the initial intent of the shaft 24 toward motion, the greater the reaction against the disturbance. As has been mentioned, a total movement of 0.005 inch of the spot across or away from the line will bring the entire output of the photocell amplifier into play, with resultant great unbalance of forces, manifesting in high velocities over minute distances, and thereby releasing the counter reaction of the power available in the oscillation control amplifier. The end practical result obtained is that no oscillation component is visible to the naked eye. w

The oscillation control system also reacts against the normal and desired motion of tracking the line; but by suitable design in a practical application of my invention, the various factors are balanced, as by making the natural period of the entire moving system relatively high compared to the velocity of the motion of line tracking; thereby applying relatively small braking or reactive force upon the normal line tracking motion, while creating large forces opposing disturbances.

The stability of the spot with reference to the line is such that power line transients, if not too marked, and the high noise leve of a powerful amplifier working under extreme conditions, and thereby containing large transient components, do not cause the spot to waver from the line, either as the line is being tracked or when the chart is stationary and the spot is in fixed contact with the line.

To minimize coupling of the several coils, which may tend to cause erratic action of the system, the planes of the coils 28 and 29 may be oriented with respect to each other and to coil by way of example, the coil 29 being shown at about 30 to the other coils and the pole faces of its electromagnet correspondingly moved.

obviously dependent on various factors, such as the distance between the coils, and may best be determined by experiment.

If it were desirable that the oscillation control system be effective at very low frequencies, one or both of the coils 29 and 28 couldbe mechanically connected to coil 20 by suitable speed increasing means.

While I have herein shown and described a specific embodiment of my invention, I wish it to be understood that modifications may be made without departing from the spirit of my invention and that I intend therefore to be limited only by the scope of the appended claims.

I claim as my invention:

1. In a photoelectric line-tracking system: a chart havingia recorded line thereon; means for moving said chart at a predetermined constant speed; means for producing a concentrated beam of light; means for deflecting said beam toward said chart and comprising a movable member mounted in the path of said beam; means biasmotor directly connected to said member for moving the member in an opposite direction against the force of said bias; photoelectric means for energizing said motor and responsive to light defiected by the member and reaching an area of the chart free from said line, so that the forces tending to move the member are balanced when the beam is in predetermined partly-obscured relation to the line; and means for stabilizing inherent oscillation of the beam with respect to the hue, and comprising means directly connected to i said member and movable to generate an E. M. F.. a supplemental electricmotor also directly connected to said member, an electronic amplifier having its input connected to said generating means, and means connecting the output of said amplifier to said supplemental motor, said lastnamed means including means whereby substantially only the generated and amplified E. M. 13'. which is due to said oscillation is passed to the supplemental motor in a sense tending constantly to quell said oscillation.

2. A photoelectric line-tracking system, as defined in claim 1, wherein the means, whereby substantially only the amplified E. M. F. which is due to theinherent oscillation of the beam with respect to the chart line is passed to the supplemental motor, is a transformer.

3. In a photoelectric line-tracking system: a chart having a recorded line thereon; means for moving said chart at a predetermined constant speed; means for producing a concentrated beam of light; means for deflecting said beam toward said chart and comprising a freely rotatable member mounted in the path of said beam; means biasing said member in one direction; an electric motor, comprising a first element directly connected to said member and rotatable therewith, for moving the member in an opposite direction against the force of said bias; photoelectric means for energizing said motor and responsive to light deflected by the member and reaching an area of the chart free from said line, so that the forces tending to move the member are balanced when the beam is in predetermined partly-obscured relation to the line but tend periodically to become unbalanced, due to the inherent instability of the system, so that normally the beam oscillates with respect to the line; and means for stabilizing said oscillation, and comprising a second element also directly connected to said member and rotatable therewith, means cooperating with said second element whereby rotation thereof produces an E. M. F., a supplemental electric motor comprising a third element also directly connected to said member and mg said member in one direction; and electric rotatable therewith, an electronic amplifier having its input connected to said generating means, and means connecting the output of said amplifier to said supplemental motor, said last-named means including means whereby substantially only the generated and amplified E. M. F. which is due to said oscillation is passed to the supplemental motor in a sense tending constantly to oppose oscillation of the member.

4. A photoelectric line-tracking system, as defined in claim 3, wherein the means, whereby substantially only the amplified E. M. F. which is due to the oscillation of the beam with respect to the chart line is passed to the supplemental motor, is a transformer.

5. In a photoelectric line-tracking system: a chart having a recorded line thereon; means for moving said chart at a predetermined constant speed; means for producing a concentrated beam through an angle; means for deflecting said beam toward said chart and comprising a member carried by said shaft and in the path of said beam: means biasing said shaft in one direction; an electric motor, comprising a first element carried by said shaft, for moving the shaft in an opposite direction against the force of said bias;

. photoelectric means for energizing said motor and responsive to light deflected by the member and reaching an area of the chart free from saidline, so that the forces tending to move said shaft are balanced when the beam is in predetermined partly-obscured relation to the line but tend periodicallyto become unbalanced, due to the. inherent instability of the system, so that normally the beam oscillates with respect to the of light; a shaft mounted for limited rotation. line at a relatively high frequency: and means for stabilizing said oscillation, and comprising a second element also carried by said shaft, means cooperating with said second element whereby rotation thereof produces an E. M. II, a supplemental electric motor comprising a third element also carried by said shaft, an electronic amplifier haying its input connected to said generating means, and means connecting the output of said amplifier to said supplemental motor, said last-named means including impulse-transmitting means whereby substantially only that part of the generated and amplified E. M. F. which is due to said high-frequency oscillation is passed to the supplemental motor in a sense tending 0021- stantly to oppose said oscillation.

PHILIP PADVA. 

